Positive displacement pumps, in which peristaltic pumps form a subclass, are employed for pumping problematic substances in particular, such as abrasive, corrosive, slurried or high-viscosity liquids and liquid-suspended solids. Peristaltic pumps are also preferred when pumping as a primary function must be complemented with accurate metering, high hygienic standard and leakproofness. Peristaltic pumps are used widely e.g. in the manufacture of foodstuffs, drugs, oil and chemical products. In heavy industries, peristaltic pumps serve to pump, inter alia, such materials as liquids and ore/mineral suspensions.
To operate properly, a peristaltic pump must be capable of forcing a volume of a fluid medium to move along a hose/tube by way of peristaltically compressing the hose from end to end during one turn of the pump rotor while simultaneously the next fluid volume is already filling the hose. Conventionally, this pumping sequence is implemented by rotating a nonrotary shoe or pressing roller, whereby the hose is subjected to progressive compression in the nip between the shoe/roller and the peripheral wall of the pump head. Furthermore, the hose/tube/tubing is selected to be sufficiently elastic and reinforces such that the hose resumes its circular profile immediately after the compression thereby creating a vacuum in its lumen thus including the entry of the next volume of the fluid medium into the hose.
Prior a publication U.S. Pat. No. 7,726,956, the solutions of related art lacked an adjustment mechanism for setting the compressive force in peristaltic pumps. More specifically, no facility was provided for setting the compression applied on the pump hose or like elastic flow channel, whereby the distance between the rotor and the pump cavity couldn't be varied from a constant value.
However, the publication U.S. Pat. No. 7,726,956 was targeted to such a need and it discloses a peristaltic pump that comprises an adjustment mechanism. A peristaltic pump according to the publication is shown in FIG. 1. The pump comprises a pump body 1, a hose 2 and a rotor 3. The rotor 3 is mounted freely rotatable on bearings mounted onto an eccentric adjustment bushing 5. In use, the rotor 3 rotates in the pump cavity and compresses the hose 2 in said pump cavity by rolling over the hose surface thus propelling the bulk of fluid medium contained in the hose 2. With the rotary progressive motion of the rotor 3 and the hose recovering its circular profile immediately after the point of rotor compression, the hose 2 creates a vacuum that causes the hose 2 to become refilled with the fluid medium being pumped. The adjustment mechanism serves to adjust the gap between the rotor outer surface and the pump cavity inner periphery that determines the compressive force imposed on the hose. The eccentric adjustment assembly disclosed in U.S. Pat. No. 7,726,956 allows runtime adjustment of hose compression to be carried out with a calibrated torque wrench. A worm gear is shaped to be rotatable by means of the torque wrench. As the worm is thus turned with the torque wrench, an accurately set torque can be applied during rotation of the worm. With the applied torque thus being always constant, also the compressive force imposed on the hose becomes sufficiently accurately set to an constant value.